The neurotrophic effect of oleic acid includes dendritic differentiation and the expression of the neuronal basic helix-loop-helix transcription factor NeuroD2 Rosa A. Rodrı ´guez-Rodrı ´guez, Arantxa Tabernero, Ana Velasco, Eva M. Lavado and Jose ´ M. Medina Departamento de Bioquı ´mica y Biologı ´a Molecular, Universidad de Salamanca, Spain Abstract We have shown recently that the presence of albumin in ast- rocytes triggers the synthesis and release of oleic acid, which behaves as a neurotrophic factor for neurons. Thus, oleic acid promotes axonal growth together with the expression of the axonal growth-associated protein, GAP-43. Here we attemp- ted to elucidate whether the neurotrophic effect of oleic acid includes dendritic differentiation. Our results indicate that oleic acid induces the expression of microtubule associated protein- 2 (MAP-2), a marker of dendritic differentiation. In addition, the presence of oleic acid promotes the translocation of MAP-2 from the soma to the dendrites. The time course of MAP-2 expression during brain development coincides with that of stearoyl-CoA desaturase, the limiting enzyme of oleic acid synthesis, indicating that both phenomena coincide during development. The effect of oleic acid on MAP-2 expression is most probably independent of autocrine factors synthesized by neurons because this effect was also observed at low cellular densities. As oleic acid is an activator of protein kinase C, the possible participation of this transduction pathway was stud- ied. Our results indicate that added oleic acid or oleic acid endogenously synthesized by astrocytes exerts its neuro- trophic effect through a protein kinase C-dependent mechan- ism as the effect was inhibited by sphingosine or two myristoylated peptide inhibitors of protein kinase C. The transduction pathway by which oleic acid induces the expres- sion of genes responsible for neuronal differentiation appears to be mediated by the transcription factor NeuroD2, a regulator of terminal neuronal differentiation. Keywords: microtubule associated protein-2, NeuroD2, neu- rons, oleic acid, protein kinase C. J. Neurochem. (2004) 88, 1041–1051. Wehaveshownrecentlythatastrocytessynthesizeandrelease oleic acid, which promotes axonal differentiation (Tabernero et al.2001).Thepresenceofoleicacidelongatesaxons,which contact other neurons, thus mimicking the neuronal networks observed in the central nervous system. These morphological phenomenaareaccompaniedbyanincreaseinthesynthesisof growth-associated protein-43 (GAP-43) (Tabernero et al. 2001), which plays an important role in axonal build-up and is considered a marker of axonal differentiation. Oleic acid activates protein kinase C (PKC) (Linden et al. 1986; Mura- kami et al. 1986; Dı ´az-Guerra et al. 1991; Khan et al. 1992) and this appears to be the mechanism by which oleic acid induces GAP-43 expression (Tabernero et al. 2001). The signal that triggers oleic acid synthesis in astrocytes is the serum protein albumin (Tabernero et al. 2002). Unlike the situation in adults, albumin reaches high concentrations in the brain and the cerebrospinal fluid of newborn mammals (Trojan and Uriel 1979; Saunders and Mollgard 1981; Mollgard et al. 1988). Thus, the presence of albumin in the developing brain may be due to the existence of a mechanism through which albumin is transferred from the blood to the brain and cerebrospinal fluid that is active only in immature rats (Laborda et al. 1989; Habgood et al. 1992; Ohsugi et al. 1992). Also, the existence of a specific receptor for albumin Received March 24, 2003; accepted October 6, 2003. Address correspondence and reprint requests to Jose ´ M. Medina, Departamento de Bioquı ´mica y Biologı ´a Molecular, Universidad de Salamanca, Edificio Departamental, Plaza de los Doctores de la Reina s/n, 37007 Salamanca, Spain. E-mail: medina@usal.es Abbreviations used: BSA, bovine serum albumin; DMEM, Dulbecco’s modified Eagle’s medium; FBS, fetal bovine serum; GAP-43, growth- associated protein-43; H-89, N-(2-[p-bromocinnamylamino]ethyl)-5- isoquinolinesulfonamide; MAP-2, microtubule associated protein-2; PBS, phosphate-buffered saline; PKA, protein kinase A; PKC, protein kinase C; SCD-1, stearoyl-CoA desaturase-1. Journal of Neurochemistry , 2004, 88, 1041–1051 doi:10.1046/j.1471-4159.2003.02262.x Ó 2004 International Society for Neurochemistry, J. Neurochem. (2004) 88, 1041–1051 1041